1. Field of the Invention
This invention relates to a control system for internal combustion engines, which controls the operation of the engine such as the ignition timing of the engine and the intake air amount supplied to the engine, based on control parameters including engine temperature-dependent control parameters, and also to a control system for vehicles, which controls the operation of an internal combustion engine and/or the operation of a transmission of a vehicle in which the engine is installed, based on control parameters including engine temperature-dependent control parameters.
2. Prior Art
There is conventionally known a method of controlling an internal combustion engine, for example, from Japanese Laid-Open Patent Publication (Kokai) No. 55-160136, in which immediately after the start of the engine, a desired idling rotational speed of the engine is determined according to engine coolant temperature, and the intake air amount is controlled in a feedback manner responsive to a difference between the desired idling rotational speed and the actual idling rotational speed such that the actual idling rotational speed becomes equal to the desired idling rotational speed. According to the known method, when the engine coolant temperature is below a predetermined value, e.g. 60.degree. C., the desired idling rotational speed is set to larger values as the engine coolant temperature lowers.
However, the conventional known method has the following problem:
That is, a rate of decrease in the temperature TCAT of a catalytic converter (catalyst) arranged in the exhaust system of an internal combustion engine with the lapse of time after stoppage of the engine is larger than a normal rate of decrease in the engine coolant temperature TW, as shown in FIG. 1. Therefore, for example, when about one hour has elapsed after stoppage of the engine, the catalyst temperature considerably drops, while the engine coolant temperature has not dropped to the same level as the catalyst temperature. On this occasion, if the engine is restarted, the desired idling rotational speed, which is set based on the engine coolant temperature, is set to a relatively low value. As a result, the catalyst temperature rises at a low rate, leading to degraded exhaust emission characteristics of the engine. A state in which the engine is held in stoppage for a short time period as long as one hour or so after stoppage of the engine will be referred to as "short soaking" in the present specification.